Wading pools can be very useful in the summer and a simple one can be built in a day.
Step 1 - Decide the Location
Find a place to dig a shallow pit eight feet square.
Step 2 - Dig the Pit
The pit needs to be 12 inches deep around the edge. It can be deeper in the middle. Make the bottom smooth and firm.
Step 3 - Build the Pool Frame
Take the four pieces of 4 x 4 and cut one end of each diagonally, at a 45-degree angle. Nail one piece of 4 x 4 to each end of one of the pieces of marine plywood. Make sure the cut end of the 4 x 4 is at the edge of the plywood. Join the other pieces of plywood until you have a frame eight foot square. You can seal the frame before you line the pool.
Step 4 - Line the Opening
Put the frame into the hole and place it as far down as possible. The cut ends of the 4 x 4s must be facing up. There will be gaps between the frame and the soil, so fill those with soil.
Step 5 - Lay Sand in the Pit
Place a two-inch layer of sand in the bottom of the pit and level out the sand.
Step 6 - Fit the Pool Liner
Spread the plastic sheet over the frame and press it into the pit over the sand. This is the liner for the pool. Go over the bottom carefully and remove as many of the wrinkles as possible. Make folds in the sides as neat as possible and make sure the liner is pressed firmly into the corners.
Step 7 - Secure the Liner
Pour sand over the plastic sheeting around the pool or use the soil you dug out of the ground to hold the frame down. You can even use sheets of marine plywood to do the job and create a deck around the pool at the same time.
Fill the pool and you have a serviceable wading pool. This is designed to be durable and is quick to build. It should give a few months of service with no trouble. A submersible pump can be used to empty the pool to change the water.
You can install a filtration unit near the pool and have two pipes going into the pool—one for intake and one for output. A home-made filter using sand or filter cotton will keep the pool water clean.